Heavy ion beams of very high energy have recently become available at Lawrence Berkeley Laboratory, California for biomedical investigation. It is proposed to investigate their radiation-chemical properties in the context of a broad biomedical study. These beams exhibit excellent depth-dose characteristics with high LET (Linear Energy Transfer) at their extreme of penetration. They show considerable promise for use in tumor therapy, radiography and laminography, and in applications involving production of deep lesions for neurological research. For confident medical application, beam characterization must go beyond conventional dosimetry, which gives no information on the spectrum of energies and particle types produced by nuclear scattering, fragmentation and changing primary beam energy. Knowledge of the detailed pattern of energy deposition and formation of primary free radicals - the precursors of biological effect - can be obtained using techniques evolved by radiation chemistry. It is proposed to use aqueous solutions as model systems, since these have been fully studied with other radiations. Primary radical and molecular products will be measured by standard scavenging techniques for a variety of high energy heavy ions as a function of penetration, using multi-compartment irradiation cells. Because free-radical diffusion and recombination processes are expected to be important with these high LET beams, the hydrogen chemical isotope effect on the primary yields will be measured simultaneously, using tritium tracer techniques. From such measurements it will be possible to infer how primary free radical distribution and interaction depends on particle type and energy. In particular, these experiments will privide data necessary for calculating the relative contributions of track "core" and "penumbra" components of the radical yield, and hence evaluating the most effective particle atomic number for various diagnostic and therapeutic applications.